11.1 Introduction

The accurate determination of the electrical field distribution is vitally important in the production of safe and economic designs of high voltage electrical equipment.

With transmission voltages typically 400 kV (r.m.s.), line and test voltages of 630 kV (r.m.s.) at power frequencies and 1425 kV (peak) lightning impulse, the problems of configuring the high voltage (HV) winding, leads, stress control rings and bushings of an HV transformer become apparent. On the rare occasions when something goes wrong, the consequences can be very serious. Figure 11.1 indicates the severe damage that can be caused by an HV flashover, in this case between the corona shield at the coil end of the HV bushing and a neutral lead. The insulation on the lead had been severely ruptured, and as a result a costly repair was needed.

Figure 11.1: Insulation rupture of the neutral lead (courtesy of ALSTOM T&D - Transformers, Stafford (TST))

The HV transformer is only one of many examples that show the importance of designers having analysis techniques capable of assessing or revalidating their designs accurately under all anticipated steady-state and transient operating conditions.

Besides the quasi-electrostatic problems associated with HV equipment discussed above, there is much interest in, and concern over, the large voltage gradients that occur along the end windings of machines fed by inverters. The inverter voltage waveforms, seen by the end windings, contain high harmonic components that can lead to sparking and erosion at the...